* Co-founder Head working with Williams (NYSE:WMB) again
* Former champions struggling at back of grid (Adds Russell, Davidson quotes)
MANAMA, March 29 (Reuters) - Williams co-founder Patrick Head has returned to the Formula One team as a consultant after they started the season with an uncompetitive car that even their own drivers say is fundamentally flawed.
The 72-year-old Briton, who founded the team with Frank Williams in 1976 and oversaw a string of title-winning cars in the 1980s and 90s, stepped away in 2011 but retains a nine percent shareholding.
Williams finished last overall in 2018 and technical head Paddy Lowe, the man who had ultimate responsibility for this year's car, left on a 'leave of absence' before the season started.
The British team said at the Bahrain Grand Prix on Friday that Head, famously blunt in expressing his opinions, was "currently offering some support to our engineering team on a short-term consultancy basis."
A spokeswoman said he had started this week at the Grove factory.
"I think it will be great," the team's British rookie George Russell told reporters. "He's a very strong character, with a lot of personality and maybe that's what we need at the moment.
"With all of his experience and the history he has at Williams, just having him around will lift everybody."
Williams, the third most successful team in Formula One history with nine constructors' crowns and 114 grand prix wins, have not won a race since 2012.
They face an uphill struggle with a car that was more than three seconds slower than Ferrari (NYSE:RACE) in practice in Bahrain.
"It doesn't take just one person to turn a team around," said former F1 driver Anthony Davidson, a pundit for Sky Sports television.
"As experienced as Patrick Head is, I can't see him turning up and making that difference with just cracking the whip a bit, which he's renowned for. A touch of the old school? Who knows. It might work but I have my reservations about it."
The car was also late to be finished, missing the first two days of pre-season testing, and spare parts are in short supply.
Deputy principal Claire Williams, daughter of Frank, played down concerns expressed by Polish driver Robert Kubica who said on Thursday that he would have to play safe on track to avoid any damage. we've got a little bit of a backlog from not having got the car out when we needed to in testing but everyone's worked really hard at the factory to make sure we've got the spares we need," Williams told Sky Sports television.
"We've got spares for all the parts that we need. We've just got to make sure that the drivers don't do anything on track to jeopardise that," she added.
"I think a lot of teams at this time of year anyway are in a similar kind of position, clearly we didn't help ourselves but it's not anything that I'm overly concerned about."
Russell, last year's Formula Two champion, said in Australia that the car had a 'fundamental problem' that would take months to fix. (Writing by Alan Baldwin in London, editing by Christian Radnedge, Pritha Sarkar and Toby Davis)